(a) Technical Field
The present disclosure relates to thin film diode array panels using metal insulator metal (MIM) diodes as switching elements, and a manufacturing method of the same. In more detail, the present disclosure relates to thin film diode array panels of a dual select diode (DSD) type, and a liquid crystal display using the same.
(b) Discussion of the Related Art
A liquid crystal display (LCD) is one of the most widely used flat panel displays. An LCD includes two panels provided with field-generating electrodes, and a liquid crystal (LC) layer interposed therebetween. The LCD displays images by applying voltages to the field-generating electrodes to generate an electric field in the LC layer, which determines orientations of LC molecules in the LC layer to adjust polarization of incident light.
An LCD may have switching elements to switch voltages of pixels arranged in a matrix form. An LCD can display various images since pixel voltages are individually switched. An LCD having switching elements to switch pixel voltages individually is called as an active matrix type LCD.
Thin film transistors or thin film diodes may be used as the switching elements. When thin film diodes are applied, MIM diodes can be used.
A MIM diode has two metal layers and one insulating layer interposed between the metal layers and a thickness capable of being measured in micrometers. A MIM diode may act as a switch due to the electrical nonlinearity of the insulating layer. A MIM diode has two terminals. As a result, the manufacturing process of the MIM diode is simpler than that of the thin film transistor having three terminals. Accordingly, MIM diodes can be manufactured at a lower cost than thin film transistors.
However, when diodes are used as switching elements, the uniformity of image quality and contrast ratio may be degraded due to asymmetry of an applied voltage with respect to the polarity.
In response to the asymmetry, a dual select diode (DSD) type panel has been developed. A DSD type panel includes two diodes which are symmetrically connected to a pixel electrode and are driven by applying voltages of opposite polarities.
A DSD type LCD shows improved image quality, contrast ratio, gray scale uniformity, and response speed by applying voltages having opposite polarities to the two diodes which are connected to a same pixel electrode. Accordingly, a DSD type LCD can display images with high resolution like that of an LCD using thin film transistors.
In a conventional DSD type LCD, scanning signal lines, diodes, and pixel electrodes are formed on a lower substrate, and image signal stripes are formed on an upper substrate. Therefore, scanning signal drivers are connected to the lower substrate and image signal drivers are connected to the upper substrate.
Known structures of DSD type LCDs make it difficult to load driver integrated circuits (ICs). Further, conventional DSD type LCDs do not provide for the wide viewing angles that are becoming more important as the size of a display increases.